package grub-efi-amd64-signed 1.142.8+2.04-1ubuntu26.6 failed to install/upgrade: installed grub-efi-amd64-signed package post-installation script subprocess was killed by signal (종료됨)

[Anselmo Park]

When I command 'sudo apt upgrade', the progress bar stopped at 91%.
A kworker related to grub consumed 100% CPU. (It uses only one CPU. The others were idle.)

Dmesg message had error about watchdog and it occurred repeatedly.

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: grub-efi-amd64-signed 1.142.8+2.04-1ubuntu26.6
ProcVersionSignature: Ubuntu 5.4.0-52.57-generic 5.4.65
Uname: Linux 5.4.0-52-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.10
Architecture: amd64
CasperMD5CheckResult: skip
Date: Wed Oct 28 11:11:25 2020
ErrorMessage: installed grub-efi-amd64-signed package post-installation script subprocess was killed by signal (종료됨)
InstallationDate: Installed on 2020-10-03 (24 days ago)
InstallationMedia: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
Python3Details: /usr/bin/python3.8, Python 3.8.5, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: N/A
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.2ubuntu0.1
SourcePackage: grub2-signed
Title: package grub-efi-amd64-signed 1.142.8+2.04-1ubuntu26.6 failed to install/upgrade: installed grub-efi-amd64-signed package post-installation script subprocess was killed by signal (종료됨)
UpgradeStatus: No upgrade log present (probably fresh install)